flint



June 17, 1947. E. F. FLINT 2,422,348

MEDIAN VALUE DEVICE IN A SIGHTING INSTRUMENT File d Jan. 29, 1945 2 SheetsSheet 1 EDWARD F. FLINT INVEN OR 4.42. BY g ATTORN s Patented June 17, 1947 Mnnmnvannn*nEvIcEam nsmn'rmes I STRUMENT:-

EgwgrghF Flint Rgphester, NzY; assignor to Bauseh {Lamb ,Olltical Company; Rgchestep This: invention relates tor caleulatinge devices andmoreparticulanly-tosueh adevicebfonnbtame. .7 ing theme'dianvvaduexofsa rigroupf;ofsquaintitative measurements.

Frequently sit beeomes-desirablemoudetermines some single value which will?be-representa$i1ze of; the separate'values-ofi a--gmup of quantitative:

. measurements. Severmmethod's -are known fen finding a value of thischaracter== One method frequently used is-zto-dfrvide-the-lq sum of the: measurements by' the numberr -of measurements 0; the group; to "find the average;- Although device have-been; heretofore preposed for detrminingthe-- average; of; an g-rfpupof measurements or the like; they-are not suittble 5;.

in some applications they are gene ra11y intni cate and; d 'rficu1t;to -keepfimp'rOp r-;a;oljustnrerit; partiqularlywheresubjeet tg hard usage:

n th r me h d: it e; sed, he: edi

et od s bas ca xfiesi n d qa q t inhl' s r s n ativ aluer rt rew. wmn w f f umbe i "measu m nts he m d a es-r b a nedeby; he kin ffmfifil fef mentss her orwm an m ndin r ss endin r ment 7 s, re med; 1 example, as rpun, seven measuremen s-t e ian al el il fl ei he o rthi. lar estmeasureme t q 'the roun,

The; devicepiatkre present inyentinn is p rticu; larly mei m: .usee i zh an mum n instrument ,f-orfl.mfiafinning theengular elemtro gof tial s sior calculattien fussr in nav ation;- tO ine he: npsit qnr f ihe g ib een er rela ive to ,the I, earths surfa lcer Accurate 'nayiggtinn, ,de=,.

pe d o a er ilalf e x enton hwccm'acy ith? 3 wh han observe antde erm ehis positienrwith; la iont asomee elestia zhfldy an, xeasethe cc r y ih;measnremnt= i heenguhnvale; vation ot the bod zan; bbservIiwill. take." a 's'eries can-$ 4. 4 I toindiegtegto th ,lobseryver tha t.hghadlta kenjhe byine ogtantpgnuns .the device is, rugged; it can be}used in cqnneptipn with' octa nts nesig neggfor. use in aircraft navigation;

evde ef mhe present invention comprises a. number of movable indicating members ofga u ben ufii i ntior eamf re r se t mfifi lllfiment in the group of measurements taken. The memberssarenerma lly. heldtinqaunull pQsitmnb-nt I v eri telys ea gjmr mqvement u at, the wil beJnQS/feibywa uatiqn rrthepne atmae im fldir eetie qand. ta; nltne directipn andtmag; nitude of the mqvamg ktLogihenperating,meansgu hus the relativemdisnlanemen of e h -m mb r ndi atesyihg,relatiye magnitude of the. mee sure mnt fitekeninttne series..,, Eacmindm ng me ber carries an, index-r mark Which wi11, ;be visible tQ .the.obQrYer andmeans armprovidedqwheljebye. h m di fihi fi' atiml tai n 'd ndq m isg ane ve .Inn-laidwithe m r. ransl ii the ,relatwe value o: .th e indve'xxnarrk,representa;, tivie of. the, .median p'f. the me?isulennents int 0 reatst numhe ot measurementsnwhielr cpuldebeg reeo'rqe q by tne-wrne dia ime, such; astmeanlsfl Q mu nsth sen h f l ez nstmm ntg;

m d anmlu iottag e esiof izeasms rntszi l li 59; 'msm wmwnnrse n ;m s

3 but in the form of the invention now preferred, the occluding means comprises a shutter normally held out of the optical path of the instrument, but movable into the same by the means releasing the indicating members after the last of the indicating members has been released. Thus, an observer using the instrument of the present invention will be unable to take a greater number of measurements than the number for which the median device is designed.

To simplify the use of the invention, the shutter is automatically moved out of the optical path of the instrument by movement of the releasing member to its position in which the indicating members can be again locked against movement.

Other objects and advantages of the present invention will appear from the following description taken in connection with the accompanying drawings in which: i

Fig. 1 is an elevational view of an bodying the invention with a portion of the casing of the octant broken away to more clearly illustrate the device of the present invention.

Fig. 2 is a front view of the octant embodying the present invention with a portion of the median device and adjacent parts of the casing of the octant broken away and cover plate 48 removed. I

Fig. 3 is a section taken along line 33 of g. 2.

Fig. 4 is a section taken along line 44 of Fig. 2.

The device of the present invention, referring now to the drawing, has'been illustrated in connection With an octant for measuring the angular elevation of a celestial body but it is to be understood that the device may be used in connection with other measuring instruments.

In the form of the invention illustrated, referring now to Fig. l, the octant comprises an index reflector l0, pivotally mounted on the casing II and adapted to reflect light rays emahating from a celestial body to the optical system of the instrument which includes an objective IL for formingan image of the celestial body. The position of the index reflector may be adjusted by means of an operating knob [3 which through shaft l4 and a gear train, not disclosed, rotatably moves the index prism' ID in a recess formed in the front face of the instrument. The knob I3 is mounted on the underside of the instrument and in the use of the instrument is actuated by the left hand as the observer holds the ocular tube IE to his eye by the handle I6 which he grasps with his right hand.

The shaft l4 carries a gear ll which meshes with and drives a gear l8 carried by a shaft 19, driving a register 2| provided with a window 22 through which the indicating members of the register are visible. It is now preferred to have the register 22 calibrated to read in degrees the angular position of the observed celestial body above the horizon. A suitable scale 23 carried by the operating knob l2, indicates theminutes of the angular positions of celestial bodies above the horizon and as usual in scales of this type, an index or fiducial line 24 is formed on a stationary member adjacent to the scale 23.

It is now customary in the use of instruments such as here illustrated to take a series of measurements and then through arithmetical formula find the average of the measurements taken or by some suitable mechanism determine the average or medianvalue of the series of measurements. This practice makes for a more accurate octant em 4 measurement and reduces to a minimum the effects of error.

In my application, Serial No. 412,275, filed September 25, 1941, I disclose and claim a device, for determining the median of a plurality of successive measurements of an instrument such as an octant, which forms a now preferred element of the combination of the present invention. The median device will not, therefore, be described in detail, for this device is fully described and claimed in my prior application above identified and only such details of thedevice will be recited here as are necessary to the understanding of the present invention.

- In the preferred form of the device of the present invention, the median device is driven by the shaft I9 through the gear train I! and I8, and the indicating members 25 of the median device are carried by the shaft I9. The indicating members, as well as the other mechanism of the median device, are mounted Within a suitable housing 26, which is secured by screws or other fastening 21 to the housing I I. A semi-cylindrical window 28 of transparent material allows an observer to view the indicating members 25.

The indicating members 25 in the form of the invention illustrated comprises discs, each one of which, best shown in Fig. 4, is provided with a notch 29 in its peripheral surface. The number of discs 25 carried by the shaft 13 is limited only by the practical size of the median device and in keeping with the basis of median determination, I preferably employ an odd number of discs 25, fifteen of these indicating discs being illustrated in the drawing.

While the discs 25 are loosely placed upon the shaft l9, they are normally held thereon for rotation therewith by a lurality of friction washers 3| carried by the shaft l9 intermediate the indicating discs 25. Each washer is provided with a lug or projection 32 which cooperates with a longitudinal groove formed in the shaft [9 and keys the washer to the shaft. The hub 33 of the gear [9 serves as a washer at one end of the shaft and takes the thrust of the disc assembly created by a spring 34 carried by the shaft IS. The spring 34 seats on a cap 35 which journals the one end of the shaft l9 and acts against the uppermost washer 3| as viewed in Fig. 1. The friction between the discs 25 and the washers 31' should be such as to cause the discs to rotate with the washers as the shaft is rotated. It is to be noted, however, that the engagement between the shaft and each disc 25 is of such a nature that the shaft may be rotated relative to any disc which is held in a fixed position.

The discs are normally held against rotation with the shaft by a plurality of spring arms 35, each one of which carries a finger 31 which when received in the notch 29 of the disc holds the same against rotation with the shaft IS. The spring arms 35 are fixed to the casing at one end thereof by screws 38 while the upper ends thereof project into the path of movement of a slide 39 operating in a guide or channel 40 formed by ridges integral with the wall 4| of the casing H, seen in elevation in Fig. 2 of the drawing. The slide 39 is formed at the one end thereof with a cam surface 42 which is adapted upon engagement with the spring arms 36 to cam the same to a position in which the fingers 31 thereof are moved out of engagement with the notches 29 of the discs 25.

In the use of the median device of the present invention, the indicating discs 25 are to be freed for rotation with'th'e shaft IS in a consecutive ifif i fifik' 5 6; order beginning witht the-uppermost.discafi'iasi Theindicating;discs-53m the formwoiitheeinel. viewed in -Figs.- 1 and 2', and Working down r vention snowpreferredaaresusedtol ndicate thee wardlii untilallot lthediscs-have;been freedio w' relative magnitudes of: them suocessrve.-. angular,

rotations adjustments eofathearefiector l Land to this end.

To movetheslide '39:dQWnW&I d1y-Ofth&instill: each...disc-,-carriesr-anlindexJm-ark. 55a The mark ment-andseriately release the.discs, the onesur-w may,comprisetanysdiscernible indication desired, face or thel-slide39sis formed with a pluralitytoia suchlas asmallhgrooveeor; notch: carryingz-a fillepteeth lk engaged by aspi ing-pressed pawl-A5 :r'oof :some.-materalrofs a color whichwill-contrast-:

tatably mounted-on alever ls havingone end-vpivew withl-thescolor.ofitheldiscl Ifzdesired;v thefilling: otallgv mounted atd l to-theacasing! L: The fneew 10,: material.:cou1d "be ;.a luminous paint containing end otthelever 4&projects throughaslotiformed some .radiumesolthatlthe markswouldebe read-- inia -plate 48 covering the slidel39-and'has fixed: ilytseen-ein;themdarke theretoone-end -of a flexible cablel49 operating in Theimarks are lsol formed on.thediscs 2 5 that a sheath- Ed-extendi-ngaround the interiorsur-face they. .-areeinalignmentawhen the discs are locked of the-hand1e-l6e A tube lit-extending. down 5 against movement: and in the illustrated formof wardlywfrom the top surface. of athe handle J6 the devices-are disposed behind-afiducial line 56 h9aSeSaspring3 n m o rmallyholdina formed-ton the ltra-nsparent window 28 :of the; a small plunger fl=in an elevated position.- The housing 26; plungeris =co n nected to--theiopposite end ot-the It will be seenrnovwthat upon release oithe first flexible cable ie and--it -may -be p e gainst" disc the index mark 55 thereof will'be moved the action of t e Spring to mOVe the Cable-491 out-ofalignmentwith-the-remainder-of the index" throughthe -sl letllll 5u nd l0ck' the 16Ve1 -45. marksiby rotation of the shaft-I9- tl' ro gh opera, Movement-oi the plunger-is Jimitedto-thatnect t knob .13 t l ting; the second ess ary tmrock the lever-46 a distance-suffi ie operation-l- When-thesecond disc is released; the tocause the pawl:45tomove-upwardly,as vieweds. 25 relative position between the index mark; of the in-L'Fig. 2 ,-fla;distance equal to one-tooth onthe first--discandthatoi the second disc is main slide -39: I ta-ined-upon rot-ationof the shaft l9 since both 53 a,- spring--53,-having one end fixed to-thecasthefirst andseconddiscs will-moveor rotate ,to:v ing II with the opposite end-cennected-to-the gather; In --fac t-,- aswill later become apparent, s1ide-39,- -tends tohold thelatten-inah -elevated 30, any i d k whi has bggn gisplqggdjljom pesitiontasecond r nsr e -p w -n its initial alignment will" throughout the revidedafor he1ding the -slide-39--against upward maini g operation of the mediandevicetmaintain movemen-t as the pawl 45 is moved out of hold: itsrelative-displacement with respefit to theinde r ingenga'gement-"with-" one; of--the-teeth-- M upon mark onthe -next -adjacent disc afterthis disc actuation; ofthe-lever: t will hu -be 5 has been released for rotation with the shaft j9;,- that through the n m: 1 sc the Thus the relative displacement between the firse indicating discs-25 can be -seriately releasedior andsecgnd ind exma rks will remain unchanged; movement; with the-shaft-- [9 by successive-d8: fromthat'w-hichexistedkbetvveen the marks after pressions of the plunger 52. the second observation'and while the second in;

Inathe use of the device of the present invendEX- IIlQXkWQSlI} its initial or aligned position tionthe, observer afte'r --sighting--the instrument It-hence follows that the separation of these, ont-a celestial body actuates the operatingknob tw marks is a measure of the difference between I i'zunti-lithe imageof thebody. formed -vby-the op the first and second observations I and that the ti-calcsystemfloretheeinstrument"is broug-htinto first index mark may be considered asrepresent coincidence rw ith adatum plane such asthe hub-- ing" the -first observation and the sec ond,,index ble -of a-liqu-id bubble-level-forming an artificialmark the second observation. horizon,--or-.the natural hQPiZGIFh'dBDBHdiHg on th'e' As the first disc is not released until after the conditions undeI- Which'the instrument---is=-used= first observation has been made, there is n9 Afiieracoineidenee has'thusbeen made; he de necessity for an observer to consultthe register pressesthelever-Satereleasethe uppermost-disc 9 22-and it-isimmaterial where the register and 2&:for=rotation-with the shaft I9 which is drivenhence the reflector IE ;is set priorto any series otj throughthi first or: gear train 1 land lB from-the observations. sh'ait l lzcarrying the operating knob|3; On the A-fter-thelast disc has been released fQIf mOYfi-g e d-emanipulation -of the--o1qerating knebl ment with" the shaft" l9, any movement o1'j the to-aaainbringtheimage of the-bodyinto coinsame will displace all of the discs relative to their cidencewithuthedatum plane,'thefirstreleased initial positionof alignment by equal amounts so disc: will =mevewith the shaft l9-commensurate that --their relative positions with respect to each with*-the\amou-nt--0f movement of the-operating other;will remain unchanged. Thus the disv knob J3 necessary-to bring the observed-body into; placementbetween any two index markswhether coincidence-withtthe artificial or naturalhorithey are adjacent or not, Will'bB a measure of the zen-a Asthe first released disc wilt-rotate with diiierence in the value of the reading which the thee-shaft duringthe-second observation anyparticular marksrepresent. peintiorareference on the first indicating -disc It will nowbe apparent that the ratio between will; be displaced-from=itsinitial position -by--an the gears-l7 and IS-is immaterial to the opera: amount proportionaltothe-movementof the 651 tion of the-device. However, the-mammumdis; shafite-laior-thesecondobservation. The second placemen-tof any index mark 55 whenmoved observation. being'completed andthe second disc; from its-initial position will'depend on tth slgear released,- the-operatingknob 13 is again actuated ratio. This ratio is preferably selectedgto acandeaiterscoincidence has; beenobtained, the commodate the maximum displacement tobe plunger fil isagain depressed to release a third normally expected ior any mark in order that; disccfor'.movementwith the shaft-J9,- the lever each-indexmark'may be observed throughthe 52: being depresseddmmediatelyfollowingthe window 28 ;after ithas been displaced from its, making of each-observation-of the series tofuninitial position.

or release the -indicating member corre The-determinationof the median value of jthe spending. to that observatiomobservations or measurements, the relative magnitudes of which are represented by the relative positions of the index marks 55, is made by merely ascertaining which mark is disposed in the middle of the series of marks. That is, which mark is positioned so that half of the remaining marks are disposed on one side of the same and the other half on the opposite side. In the device illustrated, fifteen discs have been shown and the medial mark representing the median value of the observations represented by the mark will be the eighth mark in either ascending or descending order. When the medial mark has been determined, the operating knob I3 is actuated until the medial mark is brought into coincidence with the fiducial line 55. As the register 22 is driven by the shaft IS, the register will also be operated by actuation of the knob 13 and the latter will indicate directly the value of the median of the observations in degrees.

It is possible for unequal numbers of index marks to be located on opposite sides of the fiducial line if several of the index marks are in alignment after completion of a group of measurements. In this instance, the same procedure is followed by counting from one extreme to the eighth index mark. The fact that several marks may be aligned is immaterial and they are counted as separate marks. Should one or more index marks be in alignment with the eighth or medial mark, they are also set on the fiducial line in evaluating the median.

Although actuation of the operating knob l3 after the fifteenth disc has been released will not affect the relative position of the discs and consequently the accuracy of the median value when determined yet as an average time of the day must be determined for the median of the fifteen readings, the time of the first and fifteenth reading must be computed. Thus, if eighteen observations were inadvertently made, the average time would not be the average for the series of fifteen observations because the time is determined by observing a watch prior to the first and subsequent to the last observation.

Heretofore an observer was forced to either mentally note the number of each observation as it was completed or after he had completed what he estimated to be the last observation inspect the median device to ascertain if he had actually taken the number of observations for which the device was designed. In either case, some time was lost in completing the desired number of observations and if a greater number of observation were taken, the error just discussed was created.

To prevent the possibility of this error, means are provided in the present invention for indicating to the observer when the last disc has been released and the final observation completed. In the broader aspects of the present invention, this means may comprise any signal means for advising the observer that the final observation has been made. In the preferred form of the device, however, this means comprises a shutter 58 automatically moved into the optical path of the instrument for occluding the same at the completion of the series of observations.

The shutter 58 is preferably actuated by movement of the slide 39 and to this end the latter carries a pin 59 operating in a slot Bl formed in the inner side of the cover plate as and adapted to engage the shorter arm 52 of an L-shaped lever 63, the longer arm 64 of which is pivotally mounted on the wall 65 of the recess formed in a front face of the instrument. The arm 62 projects through a recess 66 formed in the cover plate 48 and into the path of the pin 59 to be,

v(53 clockwise as seen in Fig. 1 against the action of a spring 61 carried by the pivot pin 68' on which the lever 63 is mounted. This movement of the lever causes the free end of the longer arm to be moved out of engagement with a detent on an arm 68 as described below. This arm 68 is pivotally mounted at one end thereof on a pin 69 carried by the wall 65 and a spring, not shown, normally urges the same in a counterclockwise direction. The shutter 58 is carried at the free end of the arm 68 and is moved into a position, above the lens 12, in which it occludes the optical path of the instrument when the arm 68 i urged by the spring from its position as shown in full lines to that shown in broken lines in Fig. 1.

To prevent the arm 64 of the lever 63 from inadvertently releasing the arm 68, the latter is provided with a detent H formed preferably by partially cutting an edge portion of the same and then bending over the partially cut section. The detent thus formed engages a seat '12 formed on the arm 64 of lever 63 by blanking out a portion at the free end thereof,

It will be seen, referring particularly to Fig. 1, that as the pin 59 engages and urges the arm 62 of the lever downwardly, the free end of the arm 64 will move upwardly and swing the arm 68 in the same direction until the detent H is displaced relative to the seat '52 'to a distance sufficient to permit the arm 68 to swing the shutter 58 downwardly as viewed in Fig. 1 to overlie the objective l2 and occlude the light path to the eyepiece of th instrument.

A leaf spring 13 fixed at one end to the casing of the instrument limits the swinging movement of the arm 68 and to some extent cushions the shock of the stop. This spring is engaged adjacent the free end thereof by a plunger 14 slidably mounted in a boss I5 carried by the cover plate 48. The plunger i normally held by some suitable resilient means such as a spring, not shown, in the position illustrated in Fig. 1, but is movable against the action of the spring to urge the leaf spring l3 and the arm 68 to the left as viewed in Fig. 1. Thus the plunger 14 is used to return the arm 68 to its position wherein it is engaged and held against movement by the arm 64 of the lever 53. It will be obvious now that by merely pushing the knob 16 of the plunger, the arm 68 can be returned to its engaged position.

To simplify the operation of the device of the present invention, the plunger T4 is also used to reset the median device. The plunger 14, as best illustrated in Fig. 3, is cut away to form a cam surface TI movable into engagement with a leaf spring 18 fixed at 19 to the casing and extending downwardly thereof and engaged by the pawls 35 and 54. The cam 11 upon movement of the plunger 14 cams leaf spring '18 to the right as viewed in Fig. 3. The casing is cut away at 81 to permit the spring 18 to be forced over a distance sufiicient to move the pawls out of engagement with the teeth 44 of the slide 39 whereupon the spring 53 moves the slide 39 back to its original position. This movement of the slide 39 to its original position permits the spring arms 36 to return to their normal position or at least to a position in which the fingers 31 thereof engage the peripheral surfacesof the discs 25. With the stiein'g arnis 'sli'ait irt/111' rotate z =retur nin said cam 'means to a Y retracted "positherein are brought 'i'pp osit the 'iin'grsWlfiwhich ion' whe'reby'saiddecking means; "camen'gag' 'said will then snap into place to hold the indicating ridicatiiig' members, operation of said-actuator The instrument is now reset and a second series i-n "sal=d"=-holding-ineafns is '"operative' to'jhold said of observations can be maae at any time desired, occluding rin'eans out ofthe obticahbath of*said the mediandevice-beingagain operated 'as hereinstrument. 7 1

tofore explained. V a a 10 .2:-'"lin a -deviee fOFfl'eteIHiiiIi-Iig the media'n o-f It will be obvious that measurements or ob- -asseris 'of nieasurements of an "instrumenuhavservations er a nnmeer iess "the capacity i'ng operating' means successively; moved-'for makof themedian device can-'bewi orked by the :mechding sa'i'dcmeasurements,va pluraility of movable f anismI -have shown. For example, if tl'l'evdevlce indicating r membersnfranumber-equal-to*the is operated only nine times, only nine indicating number of measurements of the series; means members will be freed for movement, but the for locking said indicating members against median of the nine values ma be located or deov t in a l p s ns va l termined in the manner already described. The from n t a position for seriately releasi fact that six of the indicating members or discs said d ca rs s e h me r ent are not released will not interfere with the oper- 0 of the series is made; means operatively connectation of the mechanism to find the median of ins s i op r in m ns and said members the nin values which have been recorded, whereby the indicating members as released are It should also be noted that my invention is moved independently in accordance t th not necessarily limited to evaluating an odd nummovement of successive t at s 0 the Op ber of measurements, Where there is a group etins ns; n lly i a tiv si nal means; composed of an even number of observations means actuated by movement of said releas greater than two, there will be two middle values means to release t l f the indicating represented by t position of t t middle bers for rendering said signal means operative index marks The median for such a group is whereby the user is apprised that measurements readily determined by rotating the shaft l9 to 0 equal to the number indicating members have cause the middle index marks-to be located at been Completed; means for determining e equal distances from but on opposite Sides f median value of the group of measurements int fiducialline. v dicated by the relative positions of said mem- From the foregoing it will be apparent that I bers; and other means for returning said releashave provided a median device of simple design m a t the Said initial position h h and operation which is adaptable for use in many 531d mdlcatmg members can be relocked 1n Sald field of use Besides adaptation t t navi null position, said other means includin means gation instrument disclosed it can be used in for rendering said signal means again inactive. any optical measuring instrument and while the In an angle measuring instrument a ng present preferred embodiments of the invention means estabiishing an angularly mOVable h v b illustrated and described herein it is line of sight with operating means for moving the to be understood that the invention is not limline of s ht. a plu ality of indicating members; ited thereby but is susceptible of changes in form means for locking ea-Ch indicating member and detail Within the scope of the appended against movement; cam means movable from an claims. inactive position for seriately disengaging said Iclaim: locking means means for moving the indicating 1 I a device for determining the median of members as disengaged in accordance with the a plurality of measurements of an optical instrumovement of the Operating means; means for m t, a h i a shaft mounted on th 1 holding successively moved indicating members ing for rotation in accordance with each measagai st r t v displa nt up n su s qu nt urement; a pluralit of indi ati mbers movement of said operating means whereby the mounted upon said shaft and frictionally enrelative displacements of the indicating members gaged thereto for rotation th it an index indicate the relative magnitudes of successive mark on each indicating member; locking means measurements; a s means for IneVing d unted in said housing and normally engagshutter into a position in which said line of sight ing said indicatin member f r locking th is occluded; means for holding said shutter out of same against rotation with said shaft; cam the line of sight; means for releasing said shutter means movable to disengage said locking means from said holding mea s p movement of Said to successively free one indicating member at cam means to release the last of said indicating a. time for rotation with said shaft whereby the members whereby the shutter is -moved into said relative displacementof the index marks of the line of sight to occlude the same and apprise the seriately released indicatin members indicates user that a numb r of measu s s been the relative magnitudes of the completed meascompleted equal to the number of indicating urements; means for occluding the optical path members; means for determining e median of said instrument; resilient means for urging value of measurements indicated by the relative said occluding means into the optical path; means positions of the indicating members; other means for holding said occluding means out of the opfor returning said cam means to a position tical path of said instrument; means for releaswherein all of said locking means are released ing said. occluding means from said holding for engagement with said indicating members; means, said means being made operative by moveand a common actuator for rendering said other ment of said cam means in releasing the means means operative and for moving said shutter to locking the last indicating member against roa position wherein it does not occlude said line of tation; register means made operativ by rotasight. tlon of said shaft for translating the position of 4. In an observation instrument the combinathe index mark representative of the median 15 tion of a, casing, movable operating means on the 11 casing for making observation measurements, means for indicating the median value of a series of a predetermined number of measurements, said last-named means comprising a plurality of movable indicating members of a number equal to the predetermined number of measurements, means for, moving each of said members independently by and in accordance with the movement of said operating means when making each measurement, locking means normally locking each indicating member in a null position, releasing means for seriately unlocking each indicating member for movement in accordance with the movement of the operating means for making EDWARD F. FLINT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Everitt Aug. 12, 1941 Number 

